The biochemical events governing the immunologically-induced secretion of the mediators of anaphylaxis from human lung tissue and rat mast cells are being studied. Both Acetylcholine and PGF2a enhance mediator release while inducing massive increases in cyclic GMP in lung tissue suggesting a role for cyclic GMP levels as a modulator of mediator release. Colchicine suppresses mediator release from human lung tissue and rat mast cells but only after disaggregation of microtubules by cold suggesting that microtubules may be involved in mediator release. And finally, a potentially important role for the eosinophil in parasitic diseases has been delineated in schistosomiasis and is now being studied.